Molecular imaging is gaining an increasingly powerful role in elucidating pathophysiological pathways, in advancing drug discovery and in deciphering developmental processes. Multiple modalities, including optical imaging, ultrasound, nuclear imaging, x-ray computed tomography (CT), and different techniques of magnetic resonance imaging (MRI) are now being used to obtain fundamental new insights on the cellular and molecular level, both in basic research using animal models, and in clinical studies in patients.
By permitting unique optical access, the eye is particularly well suited for molecular imaging: For example, transgenic mice in which the fractalkine receptor rendered intrinsically fluorescent allowed for in vivo monitoring of myeloid immune cells within the retina and choroid by scanning laser ophthalmoscopy (SLO). Retinal cell apoptosis can be assessed by intravitreal injection of fluorescence-labeled annexin 5 in vivo, using a similar SLO technique. Intravital microscopy also allows visualizing CD11c-positive dendritic cells in transgenic mice expressing yellow-fluorescent protein in these immune cells. Adoptive transfer of fluorescence-labeled transgenic T-cells enables visualizing the infiltration of specific T cells into various eye compartments.
On the other hand, functional imaging can be provided by new MR methodologies: The deuterium MR and diffusion MRI analysis techniques permit dynamic studies of water movement in animal eyes. MRI also enables pharmacokinetic studies on ocular drug delivery, and detects biomarkers for treatment efficacy in retinopathies.
Undoubtedly, these and further molecular imaging techniques currently being developed will have fundamental impact on experimental and clinical ophthalmology and thereby on our understanding of eye disease and development of therapy in general.